信息不对称
IN 2007 the state of Washington introduced a new rule aimed at making the labour market fairer: firms were banned from checking job applicants’ credit scores. Campaigners celebrated the new law as a step towards equality—an applicant with a low credit score is much more likely to be poor, black or young. Since then, ten other states have followed suit. But when Robert Clifford and Daniel Shoag, two economists, recently studied the bans, they found that the laws left blacks and the young with fewer jobs, not more.
2007年，华盛顿州为了让劳动力市场更加公平，引入了一项新的规定：公司禁止查看求职者的信用记录。活动家们称赞这项法律是迈向公平的一步：因为信用分低的求职者更有可能会是，穷人，黑人或者年轻人。从那之后，另外十个州也引入了此项规定。但是最近两位经济学家罗伯特和丹尼弗重新研究了这项，规定，他们发现，这项法律让黑人和年轻人，得到了更少的工作，而不是更多。
Before 1970, economists would not have found much in their discipline to help them mull this puzzle. Indeed, they did not think very hard about the role of information at all. In the labour market, for example, the textbooks mostly assumed that employers know the productivity of their workers—or potential workers—and, thanks to competition, pay them for exactly the value of what they produce.
在1970年之前，经济学家们并不能在他们这个学科中，找到一些能帮助他们解决这个谜题的办法。确实他们根本就没有怎么考虑到信息在其中的作用。举个例子，在劳动力市场中，大多数的教科书都假设，厂商知道他们工人的生产力，或者是潜在工人的生产力，并且，多亏了完全竞争，就正好付给他们，他们生产的那部分的价值。
You might think that research upending that conclusion would immediately be celebrated as an important breakthrough. Yet when, in the late 1960s, George Akerlof wrote “The Market for Lemons”, which did just that, and later won its author a Nobel prize, the paper was rejected by three leading journals. At the time, Mr Akerlof was an assistant professor at the University of California, Berkeley; he had only completed his PhD, at MIT, in 1966. Perhaps as a result, the American Economic Review thought his paper’s insights trivial. The Review of Economic Studies agreed. TheJournal of Political Economy had almost the opposite concern: it could not stomach the paper’s implications. Mr Akerlof, now an emeritus professor at Berkeley and married to Janet Yellen, the chairman of the Federal Reserve, recalls the editor’s complaint: “If this is correct, economics would be different.”
你可能会认为颠覆了这个结论的研究就会立即成为一个重要的突破。在六十年代后期，乔治奥特洛夫发表《柠檬市场》，这篇论文为其赢得了诺贝尔奖，但却被当时的三大期刊所拒绝。在当时，阿诺夫先生是加利福尼亚大学的助理教授。他刚刚在麻省理工学院，获得了自己的博士学位。或许就是因为这个原因，美国经济观察和经济研究观察觉得他的论文的观点并不重要。但政治经济学期刊却有着几乎完全相反的观点：它觉得自己并不能消化这个论文中的观点。阿洛夫先生现在是伯克利大学的名誉退休教授，他的妻子詹妮特特耶伦是美联储的主席。他回忆起那时编辑的抱怨：如果你是对的话那整个经济学就不一样了。
In a way, the editors were all right. Mr Akerlof’s idea, eventually published in the Quarterly Journal of Economics in 1970, was at once simple and revolutionary. Suppose buyers in the used-car market value good cars—“peaches”—at $1,000, and sellers at slightly less. A malfunctioning used car—a “lemon”—is worth only $500 to buyers (and, again, slightly less to sellers). If buyers can tell lemons and peaches apart, trade in both will flourish. In reality, buyers might struggle to tell the difference: scratches can be touched up, engine problems left undisclosed, even odometers tampered with.
从某些方面来说，编辑是对的。阿洛夫先生的观点最终在1970年出版在《经济学月刊》上，在当时是简单却具有革命性的。假设买家在二手车市场上认为好车（桃子）的价钱在1000美元，卖家则稍少一些。而劣等车（柠檬）对于买家来说只值五百块。如果买家可以区分出柠檬和桃子，那么两方的交易都会成功。但在现实中，买家却很难说出区别：划痕会被掩饰，发动机的问题会被隐瞒，里程表也会被修改。
To account for the risk that a car is a lemon, buyers cut their offers. They might be willing to pay, say, $750 for a car they perceive as having an even chance of being a lemon or a peach. But dealers who know for sure they have a peach will reject such an offer. As a result, the buyers face “adverse selection”: the only sellers who will be prepared to accept $750 will be those who know they are offloading a lemon.
为了弥补可能买到柠檬车的风险，买家就会减少他们的报价。比如他们会为他们觉得既可能是柠檬车又有可能是桃子车的二手车，提供750元的报价。但是好车的卖家却不会接受这个报价。结果就是买家面临逆向选择：只有那些知道自己正在处理一个柠檬的卖家才会接受750元的报价。
Smart buyers can foresee this problem. Knowing they will only ever be sold a lemon, they offer only $500. Sellers of lemons end up with the same price as they would have done were there no ambiguity. But peaches stay in the garage. This is a tragedy: there are buyers who would happily pay the asking-price for a peach, if only they could be sure of the car’s quality. This “information asymmetry” between buyers and sellers kills the market.
聪明的买家会预见到这个问题。他们知道自己肯定会买到一个柠檬，所以他们只愿意出五百块。柠檬卖家得到的价格与没有不确定性存在时候的价格是一样的。但是桃子车却只能呆在车库里面。这就造成了一个悲剧：如果买家能明确的知道车子的质量的话，他们愿意接受桃子车的报价。买家和卖家之间的信息不对称杀死了市场。
Is it really true that you can win a Nobel prize just for observing that some people in markets know more than others? That was the question one journalist asked of Michael Spence, who, along with Mr Akerlof and Joseph Stiglitz, was a joint recipient of the 2001 Nobel award for their work on information asymmetry. His incredulity was understandable. The lemons paper was not even an accurate description of the used-car market: clearly not every used car sold is a dud. And insurers had long recognised that their customers might be the best judges of what risks they faced, and that those keenest to buy insurance were probably the riskiest bets.
仅仅是观察到市场中的一些人知道的比另一些人多，就能获得诺贝尔奖吗？这个问题是一位记者向迈克尔斯宾塞提出来的，他和阿克洛夫、斯蒂格利茨一起，因为在信息不对称领域的贡献而获得了2001年的诺贝尔奖。这个记者的怀疑很有道理。那篇关于柠檬车的论文，甚至不算是对于二手车市场一个精确的描述：很明显，并不是所有被卖掉的车都是劣等车。并且保险人一直以来都认为他们的顾客是最能够判断他们自己的风险的，最希望买保险的人，可能就是风险最大的人。
Yet the idea was new to mainstream economists, who quickly realised that it made many of their models redundant. Further breakthroughs soon followed, as researchers examined how the asymmetry problem could be solved. Mr Spence’s flagship contribution was a 1973 paper called “Job Market Signalling” that looked at the labour market. Employers may struggle to tell which job candidates are best. Mr Spence showed that top workers might signal their talents to firms by collecting gongs, like college degrees. Crucially, this only works if the signal is credible: if low-productivity workers found it easy to get a degree, then they could masquerade as clever types.
然而主流的经济学家对这个观点还很陌生，不过他们很快就认识到，这让他们的很多模型都变得毫无用处。进一步的突破随之而来，研究者们开始研究不对称的问题可能的解决方案。思彭斯先生最突出的贡献，就是1973年关于劳动力市场的《就业市场的信号》。雇主可能很难确定谁才是最好的求职者。思彭斯指出，最好的工人会发送他们才能的“信号”，比如大学的学位。关键的一点是，这只有在信号是可信的时候才有用：如果低生产率的工人发现获得学位很容易，他们就会伪装成聪明的工人。
This idea turns conventional wisdom on its head. Education is usually thought to benefit society by making workers more productive. If it is merely a signal of talent, the returns to investment in education flow to the students, who earn a higher wage at the expense of the less able, and perhaps to universities, but not to society at large. One disciple of the idea, Bryan Caplan of George Mason University, is currently penning a book entitled “The Case Against Education”. (Mr Spence himself regrets that others took his theory as a literal description of the world.)
这个观点让传统的观点开始重新思考。一直以来人们认为教育通过提高工人的生产力而对社会有益。如果这仅仅是作为才能的信号，那么教育投资的回报就全部流向了学生，因为他们获得了更高的工资而牺牲了少数人的利益。或者回报流向了大学，但并未流向社会。乔治梅森大学的布赖恩·卡普兰作为这个观点的追随者，现在正在写一本书叫做《教育案例》。（思彭斯先生对于别人将他的理论作为文字描述的世界深感惋惜。）
Signalling helps explain what happened when Washington and those other states stopped firms from obtaining jobapplicants’ credit scores. Credit history is a credible signal: it is hard to fake, and, presumably, those with good credit scores are more likely to make good employees than those who default on their debts. Messrs Clifford and Shoag found that when firms could no longer access credit scores, they put more weight on other signals, like education and experience. Because these are rarer among disadvantaged groups, it became harder, not easier, for them to convince employers of their worth.
信号理论有助于解释华盛顿州和其他州禁止公司获得求职者的信用评分之后的现象。信用历史是一个可信的信号：很难作假，并且据推测， 那些信用分较高的员工更有可能比那些曾经贷款违约的员工表现更好。克利福德和香农发现，当公司不能获得信用评分时，他们会更加看重其他的一些信号，比如教育和经历。因为这些东西在低能力求职者中很少见，对于求职者来说，让雇主知道自己的价值变得更加困难。
Signalling explains all kinds of behaviour. Firms pay dividends to their shareholders, who must pay income tax on the payouts. Surely it would be better if they retained their earnings, boosting their share prices, and thus delivering their shareholders lightly taxed capital gains? Signalling solves the mystery: paying a dividend is a sign of strength, showing that a firm feels no need to hoard cash. By the same token, why might a restaurant deliberately locate in an area with high rents? It signals to potential customers that it believes its good food will bring it success.
信号理论解释了所有的行为，公司会给股票持有者分红，他们必须为其付出收入税。如果他们保留红利肯定更有利，这将会推动股价上涨，因此会使得股票持有者获得一点点资本利得。信号理论解决了这个谜题：支付红利是一个信号，表明公司的强大，公司觉得没有必要留存现金。同样的道理，为什么一个饭店会故意选在租金高的低端呢？它向潜在的顾客发出信号：他相信自己美味的餐品一定能够让其成功。
Signalling is not the only way to overcome the lemons problem. In a 1976 paper Mr Stiglitz and Michael Rothschild, another economist, showed how insurers might “screen” their customers. The essence of screening is to offer deals which would only ever attract one type of punter.
信号理论并不是解决柠檬问题的唯一方法。在1976年Stiglitz和Rothschild的论文中，他们指出保险人是如何筛选顾客的。筛选的关键就是提供只能吸引某种特定“赌徒”的合约。
Suppose a car insurer faces two different types of customer, high-risk and lowrisk. They cannot tell these groups apart; only the customer knows whether he is a safe driver. Messrs Rothschild and Stiglitz showed that, in a competitive market, insurers cannot profitably offer the same deal to both groups. If they did, the premiums of safe drivers would subsidise payouts to reckless ones. A rival could offer a deal with slightly lower premiums, and slightly less coverage, which would peel away only safe drivers because risky ones prefer to stay fully insured. The firm, left only with bad risks, would make a loss. (Some worried a related problem would afflict Obamacare, which forbids American health insurers from discriminating against customers who are already unwell: if the resulting high premiums were to deter healthy, young customers from signing up, firms might have to raise premiums further, driving more healthy customers away in a so-called “death spiral”.)
假设一个车险保险人面对两者不同类型的投保人：高风险的和低风险的。他并不能区别这两者，只有投保人知道自己是否是安全驾驶者。Rothschild和Stiglitz指出，在一个完全竞争市场，如果保险人向两种投保人只提供同一种合约的话，他不能盈利。如果他这样做，那么安全驾驶者的保险金就会补贴给高风险驾驶者。竞争对手只需要提供一个稍低的价格和稍少的保额，就能将全=全部安全驾驶者挖走，因为高风险驾驶者偏好完全保额。而只留下高风险驾驶者的保险公司就会亏损。（一些人担心同样的问题会影响奥巴马医改计划，该计划禁止保险人歧视已经不健康的投保人：如果较高的保险金使得健康年轻的投保人放弃投保，保险公司只有进一步提高保险金，使得更多的健康投保人离开，进入了一个“死亡螺旋”）。
The car insurer must offer two deals, making sure that each attracts only the customers it is designed for. The trick is to offer one pricey full-insurance deal, and an alternative cheap option with a sizeable deductible. Risky drivers will balk at the deductible, knowing that there is a good chance they will end up paying it when they claim. They will fork out for expensive coverage instead. Safe drivers will tolerate the high deductible and pay a lower price for what coverage they do get.
车辆保险人必须提供两种合约，确保每种合约只吸引到它为其设计的那一部分顾客。方法就是提供一分价格较高的全保合约，和另一份有着一定免赔额的价格较低的合约。高风险的驾驶者会担心这一免赔额，因为他们知道自己很可能会自掏腰包，所以他们会选择贵的全保合约。安全的驾驶者会选择忍受较高的免赔额而付出一个较低的价格。
This is not a particularly happy resolution of the problem. Good drivers are stuck with high deductibles—just as in Spence’s model of education, highly productive workers must fork out for an education in order to prove their worth. Yet screening is in play almost every time a firm offers its customers a menu of options.
这不是一个特别好的解决方案。安全的驾驶者受困于较高的免赔额，就像思彭斯的教育模型一样，高生产力的工人的必须付费教育来证明他们自己的价值。然而每当公司为顾客提供一份选择菜单的时候筛选就在起作用。
Airlines, for instance, want to milk rich customers with higher prices, without driving away poorer ones. If they knew the depth of each customer’s pockets in advance, they could offer only first-class tickets to the wealthy, and better-value tickets to everyone else. But because they must offer everyone the same options, they must nudge those who can afford it towards the pricier ticket. That means deliberately making the standard cabin uncomfortable, to ensure that the only people who slum it are those with slimmer wallets.
举个例子，航空公司想要提价从顾客身上获得更多的利益，但又不想失去较穷的顾客。如果他们实现知道了每个顾客钱包的深度那么，他们就可以只为富人提供一等票，为其他人提供更便宜的票。但是因为他们必须为所有人提供一样的选择，他们就必须鼓动那些能够承担的人去购买更贵的票。这就意味着故意的降低标准仓的舒适度，来确保只有那些囊中羞涩的人才会忍受这些。
Adverse selection has a cousin. Insurers have long known that people who buy insurance are more likely to take risks. Someone with home insurance will check their smoke alarms less often; health insurance encourages unhealthy eating and drinking. Economists first cottoned on to this phenomenon of “moral hazard” when Kenneth Arrow wrote about it in 1963.
逆向选择有一个表亲。一直以来保险人都知道人们一旦买了保险之后就更有可能去冒险。买了房屋保险之后人们就不经常检查烟雾报警器了，健康保险会鼓励不健康的饮食。当阿诺在1963年第一次提出来的时候经济学家们才开始明白败德行为这种现象。
Moral hazard occurs when incentives go haywire. The old economics, noted Mr Stiglitz in his Nobel-prize lecture, paid considerable lip-service to incentives, but had remarkably little to say about them. In a completely transparent world, you need not worry about incentivising someone, because you can use a contract to specify their behaviour precisely. It is when information is asymmetric and you cannot observe what they are doing (is your tradesman using cheap parts? Is your employee slacking?) that you must worry about ensuring that interests are aligned.
当激励措施混乱的时候败德行为就会发生。Stigliz在他的诺贝尔演讲中指出，旧的经济学只是提到了激励机制，却对其研究很少。在一个完全透明的世界中，你并不需要担心去激励某人，因为你可以用一个合约来精确地明确他们的行为。只有当信息不对称的时候你才需要担心确定利益是一致的。
Such scenarios pose what are known as “principal-agent” problems. How can a principal (like a manager) get an agent (like an employee) to behave how he wants, when he cannot monitor them all the time? The simplest way to make sure that an employee works hard is to give him some or all of the profit. Hairdressers, for instance, will often rent a spot in a salon and keep their takings for themselves.
这样的情形就提出了委托代理人问题。一个经理如何让员工按照他的意思工作，而他却不能时刻盯着他们？确保员工努力工作最简单的方法就是给他们一些或者全部的利润。举个例子理发师经常在沙龙里租一个位置，然后确保自己所赚即所得。
But hard work does not always guarantee success: a star analyst at a consulting firm, for example, might do stellar work pitching for a project that nonetheless goes to a rival. So, another option is to pay “efficiency wages”. Mr Stiglitz and Carl Shapiro, another economist, showed that firms might pay premium wages to make employees value their jobs more highly. This, in turn, would make them less likely to shirk their responsibilities, because they would lose more if they were caught and got fired. That insight helps to explain a fundamental puzzle in economics: when workers are unemployed but want jobs, why don’t wages fall until someone is willing to hire them? An answer is that above-market wages act as a carrot, the resulting unemployment, a stick.
但是努力的工作却不原能保证成功：举个例子一个咨询公司的明星分析师，虽然做着很关键的工作，但却还是被竞争对手挖走。所以另一个选择就是支付效率工资。Stigliz和Carl指出公司可能会支付一家工资来确保员工重视他们的工作。这样的话他们逃避责任的可能性就会降低，因为如果他们被抓住然后被开除就会失去的更多。这个观点有助于解释经济学中一个基本的谜题：当工人失业想要就业的时候为什么工资没有下降到直到有公司愿意雇用他们的水平？一个解释就是高于市场水平的工资起着胡萝卜的作用，而被解雇起着大棒的作用。
And this reveals an even deeper point. Before Mr Akerlof and the other pioneers of information economics came along, the discipline assumed that in competitive markets, prices reflect marginal costs: charge above cost, and a competitor will undercut you. But in a world of information asymmetry, “good behaviour is driven by earning a surplus over what one could get elsewhere,” according to Mr Stiglitz. The wage must be higher than what a worker can get in another job, for them to want to avoid the sack; and firms must find it painful to lose customers when their product is shoddy, if they are to invest in quality. In markets with imperfect information, price cannot equal marginal cost.
这揭示了一个更深层次的问题。在阿诺夫和其他一些信息经济学的先驱们之前，经济学就假设在完全竞争市场中价格反映的是边际成本：如果定价高于成本，竞争对手就会以更低的价格出售。但是在一个信息不对称的世界，按照Stigliz的说法，赚到超额利润会驱使好的行为，否则超额利润就会流向别处。工人所获得的工资要比他在另一份工作中获得的工资要高因为他们想避免解雇。如果公司想要投资质量的话，他们就会发现因为产品质量低下而流失顾客损害很大。在不完美信息市场中价格不得与边际成本。
The concept of information asymmetry, then, truly changed the discipline. Nearly 50 years after the lemons paper was rejected three times, its insights remain of crucial relevance to economists, and to economic policy. Just ask any young, black Washingtonian with a good credit score who wants to find a job.
信息不对称的概念在那时完全改变了经济学。在柠檬论文被拒绝了三次之后过了大约50年，其中的洞见现在已经对于经济学家和经济政策至关重要。你只需要问一下任何年轻的有着良好信用评分，并且正在找工作的黑人华盛顿人，就知道了。